It is sometimes necessary to periodically monitor certain features of a structure in order to evaluate its strength and integrity. In those structures where fasteners are used, certain parameters of the fasteners, such as clamping force, may be periodically measured in order to determine whether they fall outside of tolerances that could affect the strength or integrity of the structure. For example, in the case of vehicles such as aircraft, the clamping force applied by fasteners in certain mission critical structural joints and assemblies must be maintained within prescribed limits. Periodic monitoring of fastener clamping force in aircraft may be necessary because of the tendency of some structures to relax overtime, and undergo physical changes due to work hardening and creep, all of which may result in a change in the preload of the fasteners. Where a fastener preload is found to be outside of the prescribed limits, it may be necessary to re-torque the fastener, or replace it.
In the past, limited use was made of fastener measurements, rather these measurements were largely used only to confirm that the fastener was either within or outside of prescribed engineering tolerances. It was assumed that by either re-torquing the fastener to original specifications or replacing it, the structure was returned to near its original manufactured state. In fact, however, fastener status may change materially between physical inspections and these changes may have a material impact on the health of a structure.
Accordingly, there is a need for a structural analysis system that employs a computer implemented method for assessing the health of the structure using non-contact measurement of fastener parameters. There is also a need for a structural analysis method using that may be used to establish the basis for maintenance and process/material/component improvements.